On the stability of the solar chromosphere-corona transition region

We prove the stability of a previously obtained temperature-versus-thickness distribution in the solar chromosphere-corona transition region. The temperature distribution has been obtained on the assumption that the plasma heating by classical heat flux is balanced by the energy loss due to radiation.     

Effect of dielectronic recombination excitation in the solar chromosphere-corona transition region

The intensities of lines emitted from the solar chromosphere-corona transition region and observed on the earth are calculated by considering excitation of electrons to the upper level caused by electron-impact excitation and dielectronic recombination excitation processes. For the lines under investigation, the electron-impact deexcitation rates are negligibly small in comparison with spontaneous transition probabilities. Hence, electrons from the upper level deexcite through spontaneous transition only, emitting photons of wavelength corresponding to the energy difference between two levels. To determine the contribution of dielectronic recombination excitation (DRE) to the excitation mechanism, the calculations are repeated with exclusion of DRE. It is found that DRE contributes significantly and that its contribution may be much larger than that of electron-impact excitation.     

Long-term evolution of the solar wind transition region

The results of observations of radio wave scattering due to the circumsolar plasma using several natural sources simultaneously are presented. The outlines of the inner and outer boundaries of the solar wind transition region are derived from the radial dependence of the radio wave scattering. Radio maps in the form of two-dimensional representations of the transition region are constructed to follow the evolution of the solar wind stream structure in the 11-year sunspot cycle. The results of the 1989–1994 radioastronomical observations combined with the optical corona data show that the phenomena in the immediate vicinity of the solar surface play a dominant role in the hypersonic solar wind generation.     

On the solar radiation field in a polluted atmosphere

Measurements of the fields of intensity and polarization of radiation from the sunlit sky, made in the heavily polluted atmosphere of Los Angeles, are compared with similar measurements obtained in Davis under particularly clear atmospheric conditions, and with computed fields for selected atmospheric models. Data for a thick stratus overcast are also included. The measurements are in six spectral intervals from the ultraviolet to the near infrared, the intervals being defined by interference type optical filters in combination with a photomultiplier tube having an S-20 response.     

MHD shocks and the origin of the solar transition region

Simultaneous observations of the solar atmosphere from its surface to the corona obtained with the Solar and Heliospheric Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE) show a ubiquitous sequence of events that start from cancellation of photospheric magnetic fields, pass through shock formation, and result in transition region supersonic jets and microflares. These results support a novel view of the energy buildup in the solar atmosphere associated with a cascade of shock waves produced by interacting network magnetic elements in the photosphere and provide insight into the origin of the solar transition region. The findings account for the general mechanisms of energy production, transfer, and release throughout the Sun's and stellar atmospheres.     

太阳过渡区紫外光谱的观测与诊断

太阳过渡区是太阳色球层顶到日冕底部的大气薄层。厚度仅几百千米,但其间太阳等离子体参数变化剧烈。过渡区的辐射多为光学薄的远紫外、极紫外发射谱线和背景连续谱线。由于地球大气的吸收,过渡区紫外光谱需通过天基观测才能实现。近几十年来,星载仪器的成功发射为太阳过渡区的研究打开了新纪元。工作回顾了太阳过渡区紫外光谱的观测历史和各类星载仪器,特别介绍了近十几年几种重要的光谱仪器。详细阐述了过渡区紫外光谱的发生率、电子密度和电子温度的诊断原理。讨论了过渡区紫外谱线的形状,并以SOHO/SUMER光谱仪为例介绍了表征谱线的几种重要参量及其物理意义。     

Heat-transfer mechanisms in solar flares. 1: Classical and anomalous heat conduction

In the context of the problem of energy transport in solar flares, simplified analytical models have been developed that describe plasma heating in the solar atmosphere by heat fluxes from the super-hot (T _e ≳ 10⁸ K) reconnecting current layer. It is shown that the applicability conditions of common heat conduction produced by Coulomb collisions of electrons in plasma are not fulfilled in solar flares. The heat flux calculated using the classical Fourier’s law proves to be significantly higher than the real energy fluxes known from modern multi-wavelength observations of flares. The so called anomalous flux produced by interaction of free electrons with ion acoustic waves in a plasma is critically analyzed. The question of what the dominant mechanism of heat transfer in solar flares is requires additional consideration [1].     

On a generalization of the Gibbs equation for heat conduction

A generalized Gibbs equation for the heat conduction problem is proposed in order to take finite wave speed into account.     

On the electronic specific heat of transition metals

A simple framework to calculate the electronic specific heat enhancement is presented and applied to the case of the electron-electron interaction in transition metals. A substantial contribution has been found in iron and niobium.     

On the entropy production for the Davies model of heat conduction

The formula for the entropy production in open quantum systems is examined for the Davies model of heat conduction.This work is supported by Polish Ministry of Higher Education Science and Technology, project MRI 7.     

Fast-moving radio sources in the solar atmosphere

This paper presents observations of the unusual phenomenon of fast-moving microwave sources using the Siberian solar radio telescope (SSRT). We observed two sources characterized by two features in common: the fast proper regular motion (with averaged velocity 180–200 km/s) and the long lifetime. By analyzing the instrumental and artificial interference, we conclude that the observed sources are of solar origin.     

Creation of magnetic energy in the solar atmosphere

We show that a magnetic flux tube can grow in strength and size provided the temperature increases outward at the edge of the tube where the axial magnetic field declines to its external value. The radius of the tube increases at a rate determined by our theory. It is the coincidence of temperature and magnetic field gradients of opposite sign that generates the new field, and if this is lost the tube ceases to grow. The phenomenon is illustrated by adopting plausible distributions for the temperature and magnetic field strength, which yield an expression for the rate of growth of the magnetic field magnitude B. The mechanism provides a possible explanation of the fibrous nature of solar magnetic fields.     

On the stability conditions for heat conduction with finite wave speed

Using Liapounov's procedure, stability conditions for the heat conduction problem with finite wave speed are derived.     

A model of heat conduction

We construct a model of a chain of atoms coupled at its ends to two reservoirs at different temperatures. In a weak coupling limit the atoms obey a stochastic evolution law and have an equilibrium state with a uniform temperature gradient along the chain.     

On the heat capacity at constant volume near the superfluid transition

Available experimental results forC_ν nearT_λ are examined for consistency with other thermodynamic measurements, and are compared with current theories.     

Model for heat conduction in nanofluids

A comprehensive model has been proposed to account for the large enhancement of thermal conductivity in nanofluids and its strong temperature dependence, which the classical Maxwellian theory has been unable to explain. The dependence of thermal conductivity on particle size, concentration, and temperature has been taken care of simultaneously in our treatment. While the geometrical effect of an increase in surface area with a decrease in particle size, rationalized using a stationary particle model, accounts for the conductivity enhancement, a moving particle model developed from the Stokes-Einstein formula explains the temperature effect. Predictions from the combined model agree with the experimentally observed values of conductivity enhancement of nanofluids.     

Fluctuation theorem in quantum heat conduction

We consider steady-state heat conduction across a quantum harmonic chain connected to reservoirs modeled by infinite collection of oscillators. The heat, Q, flowing across the oscillator in a time interval tau is a stochastic variable and we study the probability distribution function P(Q). We compute the exact generating function of Q at large tau and the large deviation function. The generating function has a symmetry satisfying the steady-state fluctuation theorem without any quantum corrections. The distribution P(Q) is non-Gaussian with clear exponential tails. The effect of finite tau and nonlinearity is considered in the classical limit through Langevin simulations. We also obtain the prediction of quantum heat current fluctuations at low temperatures in clean wires.     

Asymmetric heat conduction in nonlinear lattices

In this Letter, we conduct an extensive study of the two-segment Frenkel-Kontorova model. We show that the rectification effect of the heat flux reported in recent literature is possible only in the weak interfacial coupling limit. The rectification effect will be reversed when the properties of the interface and the system size change. These two types of asymmetric heat conduction are governed by different mechanisms though both are induced by nonlinearity. An intuitive physical picture is proposed to interpret the reversal of the rectification effect. Since asymmetric heat conduction depends critically on the properties of the interface and the system size, it is probably not an easy task to fabricate a thermal rectifier or thermal diode in practice.